Non-line of Sight imaging by SPAD​

Introduction

Silicon single photon avalanche detector (Si SPAD) has become a hot topic today for its single photon sensitivity, pico-second timing resolution and CMOS compatibility and low cost. Because of its unique properties, it becomes a tool to capture transient imaging for computer vision industry. One of applications enabled by transient imaging is non-line of sight problem, usually being referred to "look around the corner", where using Si SPAD, we could locate, track and recognize the shape of objects around the corner without directly seeing it.

The object of our project is to simulate Si SPAD response in non-line of sight imaging using ray tracing and verify its algorithm to track position of "hidden" object.

There have been multiple papers published on this topic. The one we have studied is “Detection and tracking of moving objects hidden from view”. It was published last year on nature photonics. The scenario they provided is as follow. First they have the SPAD and laser light source hang at the wall. Then the laser and SPAD would first hit the ground. And these two regions at the ground are our starting point and the end point.

This remains a hot area for recently years. The one we focus on is "“Detection and tracking of moving objects hidden from view".

Background

Difference between APD and SPAD

Traditional avalanche photo detector (APD) and SPAD both use avalanche effect to amplify signal. However, both of them are very different in performance. APD usually have a time resolution of sub nanoseconds while SPAD have a time resolution of pico-seconds. The gain also has a large difference: APD is around 10-100, and SPAD is above $10^6$ infinity

Methods

1) paper scene experiment 2) volumetric reconstruction

Results

1) Ray optic distribution 2) distance relationship 3) ray optics distribution verification 4) volumetric reconstruction verification

Results 4.1

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Example of two iterations of the meanshift algorithm